Manufacture of water-repellent papers or paper articles sized with wax dispersions



Patented fiec. 11, 1934 UNl'lED STATES PATENT OFFICE Oscar F. Neitzke,Belmont, Mass, asslgnor to Bennett, Incorporated, Cambridge, Mass., a

Corporation of Massachusetts No Drawing. application August 6, 1932,Serial No. 627,811

Claims.

Within recent years, great strides have been made in manufacturingwater-repellent papers through the addition of aqueous wax dispersionsto the paper pulp before it is delivered to suit- 5 able paper-formingor board-forming machines.

Sized papers or boards thus made are put to various uses, includingmanufacture into such articles as drinking cups and cartons for vendingwet food products, such as oysters, ice cream, or the like.

When the bulk pulp is sized with aqueous wax dispersions, such asparaflin wax, the dispersed particles are fixed on the pulp fibers inthe form of discrete, small particles. These particles undergo more orless fiuxing and coalescence when the sheet of paper or board formedfrom the pulp passes over the dry end of the papermaking machine. Itmust, however, be borne in mind that papermaking machines are run atsuch high rates of speed that the paper sheet is exposed to elevatedtemperature for only .av matter of seconds. Again, the paper rarelyreaches the temperature of the hot drier drums, because during most ofits travel over the dry end of the paper machine it is associated withconsiderable water, which must be evaporated from the sheet before itacquires the temperature of the drums. It is thus seen that when papersare sized through the use of aqueous wax dispersions, as hereinbeforedescribed, their wax content has comparatively little opportunity tobecome thoroughly fluxed and coalesced as a continuous phase or body inthe sheet.

I have found that the degree to which a paper or board containingdispersed wax size acquires water-repellency depends in large measureupon the fiuxing and coalescence which its wax content has undergone.Indeed, I have discovered that papers or boards sized as heretoforethrough the use of aqueous wax dispersions never develop their potentialwater-resistance on account of the inadequate fluxing action which theyhave undergone on the papermaking machine. -It is hence not surprisingthat papers or boards so made are highly inefiective against the actionof hot, aqueous liquids. For instance, drinking cups made of paper whichhas been wax-sized by adding aqueous dispersions of wax to the furnishin the beater engine leak almost at once when hot water is pouredthereinto. The same is true of cartons made from paperboard which hasbeen sized in a similar way. In other words, although such papers orboards may for some purposes be suificiently resistant to thepenetrating and disintegrating action of cold water, they are entirelyunsatisfactory when subjected to the action of hot water or otheraqueous liquids which tend to penetrate and loosen the fibrousstructure.

In working to overcome the deficiencies of papers or boards sized withwax dispersions, I have found that it is possible to developsurprisingly high water-repellency therein, provided that the papers orboards, after they have come ofi the papermaking machine are subjectedto a temperature distinctly above the melting point of the wax but shortof the scorching temperature of the paper for a substantial period oftime, that is, for at least a few minutes. When the paper or board is tobe converted into such ultimate articles as drinking cups or cartons,these articles may be subjected to the heat treatment. On the otherhand, the paper or board itself may be heat-treated as in the form ofrolls or separate sheets. While it is possible to accomplish the desiredtransformation of the paper or board in a dry atmosphere, it ispreferable that the atmosphere be laden with moisture so as to avoidcharring and embrittlement of the fibers.

In those cases when the water-repellent paper or board is to serve forthe fabrication of such articles as drinking cups or cartons for vendingwet edibles, it is common practice to use paraffine wax as thewater-repellent material, because it is tasteless and odorless andimparts a softness and pliability to the paper, comporting well withformation into curved or sharp-cornered containers. I shall thereforeillustrate the principles of my invention by citing specifically thetreatment of a paperboard containing dispersed hydrocarbon wax of theparaffin series as the sizing agent and known in the trade as can bodystock. The board may comprise any suitable fibrous base and containsizing agents, such as r0sin,'in addition to the dispersed paraffin wax.Thus, it may contain about 1% to 2% of dispersed hydrocarbon wax andabout 3% rosin size as its sizing components. Such board should beexposed for at least about fifteen minutes to a temperature of about 225to 275 F. in order to acquire a water-repellency consonant with anability to withstand the disintegrating action of hot, aqueous liquids,e. g., hot coffee or the like. A cup or carton fabricated from boardheat-treated in this way can withstand the action of boiling waterindefinitely, whereas the same container lacking the heat-treatment isattacked by boiling water and begins to leak at once. Repeatedexperiments consistently show that cartons or cups made from theheattreated papers of the present invention are well adapted to receiveboiling coffee or similar aqueous liquids and to hold such liquids untilthey have cooled to room temperature without any leakage whatever.

As already indicated, the heating chamber for the paper or board, or thefinished articles made therefrom, is preferably kept highly humid, so asto maintain the paper insoft, pliant condition and thereby to avoid an.over-dried condition associated with irreparable injury to the paper. Tothis end, it is possible to supply live steam at the proper temperatureas the heating medium for the chamber. When hot air is used as theheating medium, it is also preferably commingled with steam vapor, as byemitting steam into the chamber or by maintaining therein shallow traysof water presenting a large evaporating surface. When rolls of paper orboard are subjected to the heat treatment, it is important that therolls reach the desired high temperature uniformly throughout. Dependingupon the size of the roll, this may take some hours, but a long periodof exposure is beneficial, rather than otherwise. On the other hand,even when the paper is heated in the form of finished articles and thusquickly acquires the desired temperature uniformly throughout, theheating period should be at least about fifteen minutes, since a shorterheat treatment does not develop the maximum potential water repellencytherein. In fact, I find it better to expose the finished articles forabout one-half hour to an atmosphere heated to a temperature of about225 to 275 F., in order to ensure what may be termed an equilibriumwater-repellency in the paper. In the case of rolls of paper or boardrequiring an unduly extended heating period to reach a uniformtemperature throughout, provision may ,be made to shorten this period,as by winding the paper on perforated mandrels or cores, through whichsteam and/or heated air may be circulated so as to efiect a heating ofthe rolls from their interiors, as well as from their outer surfaces.

It is to be understood that the principles of my invention apply, nomatter what kind of paper stock is used in the body of the paper orboard. Thus, the stock may advantageously be a mixed furnish containingnon-cellulosic fibers, such as asbestos, as well as cellulosic fibers,such as wood pulp, since the papers made from such stock, especially anasbestos-containing paper is vastly improved in its water-repellencywhen made according to the present invention. Any of the conventionalways of sizing the stock with aqueous dispersions of wax may be adopted.In the case of wax dispersions which contain rosin soap or otherprecipitable stabilizer, the stabilizer may be reacted upon with alum orother suitable precipitant, so as to cause the deposition of thedispersed wax on the stock before the papermaking step. Any other methodof introducing the dispersed wax and other sizing material into thepaper may be used. In some instances, the wax dispersion may be appliedas a surface size to a prefabricated sheet of paper, as by a spraying,dipping, or coating operation, followed, if desired, by calenderingunder heavy pressure to force the wax particles into the body of thepaper. In such instances, too, I have found that the heat treatmenthereinbefore described is of great value, as it develops in the paperits maximum water-repellency impossible of attainment when thesurfacesized paper is quickly run through a succession of calender rollseven in hot condition. I have adverted to the fact that the heattreatment of the present invention as applied to papers sized withdispersed hydrocarbon wax is preferably conducted within a temperaturerange of about 225 to 275 F. This is especially true in the case of adispersed hydrocarbon wax having a melting point of about 150 to 160 F.Both the lower and upper temperature limits are of significance in suchcase, for, if paper sized with such dispersed wax is exposed totemperatures materially below 225 F., it is improved but little inwater-repellency even after prolonged exposure, whereas, if the paperundergoes much heating at temperatures considerably in excess of 275 F.,it is likely to be badly scorched or discolored and to lose its bestphysical characteristics.

Paper sized with dispersed wax, other than that specifically mentioned,may be associated with other temperature and time factors, but in eachcase it is necessary to heat the paper for at least a few minutesdistinctly above the melting point of the wax, in order to develophighest waterrepellency therein. When water-dispersed waxes whosemelting point is lower than 150 to 160 F. are employed for sizing papersor boards as hereinbefore described, one may heat the dried papers orboards to a minimum temperature below 225 F. and yet realize the desiredimprovement in water-repellency so long as the melting point of suchwaxes is distinctly overstepped and maintained for a matter of minutes.Thus, when socalled scale wax having a melting point of about 120 F.constitutes the water-dispersed size which is incorporated into papersor boards, one need heat the dried papers or boards to a minimumtemperature of only about 160 F. for about fifteen minutes to realizethe desired improvement in water-repellency. Of course, one may heatsuch papers or boards to temperatures above 160 F. to shorten the timeperiod necessary for the attainment of the desired result, so long asone does not exceed a temperature of about 275 F., which, as alreadyindicated, detracts from the best physical characteristics of the papersor boards. With a wax of given melting point, it is preferable toperform the heat treatment on the sized papers or boards at the maximumtemperature consistent with a preservation of the physicalcharacteristics of the papers or boards, since the greater thedifferential between the temperature of the heat treatment and themelting point of the wax, the shorter is the time of heat treatmentnecessary for the attainment of a given increase in water-repellency inthe papers or boards.

There are provinces of utility for my invention other than in producingfabricated articles such as cups and cartons, designed for use inconnection with aqueous liquids or wet food products at normal orelevated temperature conditions. There are instances when it is desiredthat the papers or boards as such acquire the maximum water-repellencyattainable through the use of a given amount of water-dispersed wax as asizing ingredient therein, since such papers may be used for wrappingwet food products, such as vegetables or meats, or may serve in makingbags, boxes, or other containers designed to protect their contentsagainst moisture, as well as to resist disintegration in the presence ofmoisture. For these various uses, papers or boards treated in accordancewith my invention are far more satisfactory than similar papers whichare used substantially in the condition that they leave the therefore,advantageouslyreceive the heat treatment of the present invention, inorder that their tendency to shrink and warp on account of repeatedmoistening and drying may be greatly diminished. In the case of plied orbuilt-up boards made by'adhesively securing a number of dried plies insuperposed face to face relationship, it is possible to subject eitherthe individual plies or the built-up board to the heat treatment of thepresent invention.

In carrying out investigations to ascertain the eiIect of a heattreatment such as I have described on papers or boards sized withmaterials otherthan wax, and more especially with various rosin sizeslacking wax as asizing component, it was found that the papers on boardswere improved little, if any, in their water-repellency. Apparently suchwater-repelling efiect as can be secured in rosin-sized paper is hadwhen the paper is subjected to drying as ordinarily, that is, 'as ittraverses the dry end of the papermaking machine. When dried,rosin-sized paper is then heat-treated as hereinbefore described, onedoes not significantly appreciate the water-re-.

in rosin-sized papers along with free rosin ren-,

ders the size as a whole so refractory or resistant to softening andfusion by the action of heat that it is impossible to enhance thewater-repellency of such papers without going to such high temperaturesas would discolor and otherwise injure them. What I have ,said holdstrue even of papers whereinto have entered rosin sizing compositionscontaining a substantial proportion of free or unsaponifled rosin, forinstance compositions containing as much as 25% or more free rosin.

In the appended claims, I use the word "paper in its broad sense tocomprehend not only the papers but also thick sheets or boards of one ormore plies made on papermaking machinery..

I claim:

1. In the production of papers of high waterrepellency containing but asmallrpercentage of sizing material, including wax. those steps whichcomprise incorporatin'g'into paper-making stock an amount ofwater-dispersed, solid wax and a stabilizer for said dispersed wax toconstitute such lency, and subjecting the paper in the condition that itleaves the dry end for at least a few minutes to a temperaturedistinctly above the melting point of the wax but below the scorchingtemperature of the paper, thereby causing the wax content to becomethoroughly fluxed and coalesced on the fibers and enhancing markedly thewater-repellency of the paper. I

2. In the production of papers of high waterrepellency containing but asmall percentage of sizing material, including wax, those steps whichcomprise incorporating into paper-making stock water-dispersed wax androsin-size-stabilizer for said dispersed wax to constitute such wax andstabilizer but a small percentage of said stock, adding a precipitant tofix the wax and rosin size to the stock, running the resulting stock oilon a paper-making machine equipped with a dry end and running at a speedsuch that the resulting paper is delivered in dry condition from the dryend at much lower than its maximum water-repellency, and subjecting thepaper in the condition that it leaves the dry end for at least a fewminutes to a temperature distinctly above the melting point of the waxbut below the scorching temperature of the paper, thereby causing thewax content to become thoroughly fluxed and coalesced on the fibers andenhancing markedly the water-repellency of the paper.

3. In the production of papers of high waterrepellency containing but asmall percentage of sizing material, including hydrocarbon wax, thosesteps which comprise incorporating into papermaking stock an amount ofwater-dispersing, solid, hydrocarbon wax and a stabilizer for saiddispersed wax to constitute such wax and stabilizer but a smallpercentage of said stock, running the result 'ng stock 0115 on apaper-making machine equipped with a dry end and running at a speed suchthat the resulting paper is delivered in dry condition from the dry endat much lower than its maximum water-repellency, and subjecting thepaper in the condition that it leaves he dry end for at least aboutfifteen minutes to a mperature distinctly above the melting point-ofsuch wax but below about 275 F., thereby causing the wax content tobecome thoroughly fluxed and coalesced on the flbers'and enhancingmarkedly the water-repellency of the paper.

4. In the production of papers of high water- I repellency containingbut a small percentage of sizing material, including hydrocarbon wax,those steps which comprise incorporating into papermaking stock anamount of water-dispersed, solid, hydrocarbon wax and a precipitablestabilizer for said dispersed wax to constitute such wax and stabilizerbut a small percentage of said stock, adding a precipitant toprecipitate said stabilizer and fix said wax to the stock, running theresulting stock off on a paper-marking machine equipped with a dry endand running at a speed such that the resulting paper is delivered in drycondition from the dry end at much lower than its maximumwater-repellency, and exposing the paper in the condition that it leavesthe dry end for at least about flfteenminutes to a moist atmosphere at atemperature distinctly above the melting po'nt of such waxbut belowabout 275 F., thereby causing the 'wax content to become thoroughlyfluxed and coalesced on the fibers and enhancing markedly thewater-repellency of the paper. a

5. A water-repellent paper product comprising felted fibers and a smallproportion of wax-containing sizing material substantially uniformlydistributed by fusion and coalescence over the said fibers. the saidproduct being substantially that resulting from the steps set forth inclaim 1.

